This invention relates generally to shock absorbers for oil well pumps; more specifically, it relates to a shock absorber which is interposed between the walking beam of an oil well pumping unit and the string of sucker rods which extend down into the borehole.
In oil well pumping operations, it is customary to employ a lift-type pump at the bottom of the well's borehole. The sub-surface pump is sequentially raised and lowered by the movement of a crank on top of the ground--through connection with a plurality of sucker rods that extend down into the well. A polished rod connects the top one of the string of sucker rods to a hanger bar positioned above ground level; and the hanger bar, in turn, is connected through two parallel cables to the distal end of the machine-driven crank.
It has long been known that the stress that is applied by a crank to a string of sucker rods (which may be several thousand feet long) can be very severe. And, it is not uncommon for the cyclical vibrations in the sucker rods to cause one or more them to fail after only a few weeks or months of well operation. In view of the fact that the problem has long been recognized, it is not surprising that various solutions have been tried; and certain proposals even appear in U.S. patents. Examples of U.S. patents which teach various forms of shock absorbers for use in this field include: No. 2,098,290 to Hinkle et al. entitled "Sucker Rod Impulse and Impact Damper"; No. 3,404,877 to Darnell entitled "Shock Absorber"; and No. 4,176,714 to Case entitled "Shock Absorber for Oil Well Pumping Unit." Another shock absorber has been marketed for many years by Dyna-Pak, Inc. of Florissant, Colo. The Dyna-Pak shock absorber constitutes the subject matter of application Ser. No. 148,544 filed May 9, 1980 by Paul W. Fix entitled "Sucker Rod Shock Absorber", now U.S. Pat. No. 4,354,397.
Of course, the Fix and the Case patents are the more recent ones, so it is logical that they should be describing the very latest ideas in material technology, including the use of elastomeric materials which serve to cushion shocks and damp vibrations instead of merely storing energy (as does a coil spring). However, both the Case and Fix shock absorbers have fundamental design characteristics that render them vulnerable to problems in the field; specifically, both the Case and the Fix shock absorbers have open tops and closed bottoms. It has been found that when such open-top devices are placed in harsh working environments, they tend to accumulate both water and dirt within their tubular canisters. In the winter time, the accumulated water from rain or snow falling on the shock absorber will often freeze within the canister, thereby converting a previously resilient shock absorber into essentially a solid block. Obviously, a frozen shock absorber has none of the benefits that could be obtained from the shock absorber in its new and freshly installed condition. Additionally, any dust and dirt which accumulates within the open-topped tubular bodies eventually serves as an abrasive to wear down the elastomeric materials which constitute the only cushioning material in an operating system. So, even though the concept of an oil well shock absorber has been in existence for well over 50 years, there has still remained a need for a reliable, simple and effective shock absorber for oil well pumping units. It is an object of this invention to provide such a shock absorber.
It is a further object to provide a shock absorber which is easily convertible so as to be used with polished rods having a diameter of 1.25 inches as well as those having a diameter of 1.50 inches.
These objects and others will be apparent from a study of the specification and the claims appended thereto, as well as reference to the attached drawings.